Ordering doesn't work when setting order kwargs to 0

[RobinRamael]

The constructor for ChoiceItem checks the order kwarg for truthiness instead for wether it's None, which puts that ChoiceItem in the wrong place in the ordering.

e.g.

In [5]: class SomeChoices(DjangoChoices):
   ...:         foo = C(order=0)
   ...:         bar = C(order=1)
   ...:         baz = C(order=2)
   ...:

In [6]: SomeChoices.choices
Out[6]: (('bar', 'bar'), ('baz', 'baz'), ('foo', 'foo'))

While we'd expect the order be the same as the class definition. This behavior is not mentioned in the docs.

[sergei-maertens]

input from Slack by Robin:

the bug is in the ChoiceItem constructor, it does if not ordering: orderin= some default, instead of if ordering is None